The invention concerns a hydraulically assisted steering device which is preferably suitable for use in motor vehicles, i.e. for acting upon a steering handwheel or a steering wheel in the case of a ship. According to my prior U.S. Pat. No. 4,219,093, steering may be selectively effected either by turns on the steering wheel or through a sensor monitoring a directrix. With such an arrangement, pre-control valves are actuated by the sensor. In the context of this invention they shall be actuated by the steering wheel.
Hydraulically assisted steering devices of the foregoing type must have a device for achieving a cut-out effect. Within a proportional band the pressure in one working chamber of the steering motor increases proportionally to the force applied to the actuating device. Once pressure and force have exceeded a certain limit the increase in the force shall be only slight, whilst the pressure shall increase steeply. This leads to high pressure being available e.g. for parking operations with relatively little manual force needed, whilst (although quite harmless) there are forces acting upon the steering elements (such as wheels) within the cut-out range, for which there is no feedback to the actuating device.